JP5686229B2 - Microporous membrane, method for producing the same, battery separator, and resin composition for non-aqueous electrolyte secondary battery separator - Google Patents

Description

  The present invention relates to a microporous membrane, in particular, a microporous membrane for a non-aqueous electrolyte secondary battery separator, a production method thereof, and a resin composition for a non-aqueous electrolyte secondary battery separator.

  As electronic devices become cordless and portable, non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries with high electromotive force and low self-discharge are attracting attention as power sources for driving these devices. In recent years, in particular, with the progress of higher energy density, not only conventional electronic equipment applications but also automobile applications have rapidly increased, and further safety needs are required.

  In non-aqueous electrolyte secondary batteries, a separator is interposed between the positive electrode and the negative electrode in order to prevent short-circuiting of both electrodes. As such a separator, a large number of micropores are formed in order to ensure ion permeability between the two electrodes. Or the like (hereinafter referred to as “microporous membrane”) is used. This microporous membrane has not only excellent mechanical properties, but also has a “shutdown function” that blocks the current by blocking the pores of the microporous membrane when the battery temperature rises. A porous membrane is used. However, the separator made of the above-mentioned polyolefin microporous membrane has a “meltdown” in which when the non-aqueous electrolyte secondary battery starts to run out of heat and continues to rise in temperature, it undergoes thermal contraction and breaks the film, causing both electrodes to short-circuit. There is a problem to cause.

  For this reason, the microporous membrane is required to have a shutdown function and “heat-shrinkage resistance” to prevent meltdown, but the shutdown function is based on the capping of pores due to melting of polyolefin, Shrinkage is contradictory in nature.

  Therefore, in order to improve the heat shrinkage resistance and make the shutdown function compatible, spherical fine particles having a diameter of 1 to 10 μm made of polybutylene terephthalate (PBT) having a high melting point are dispersed in a polyolefin-based phase. A microporous membrane has been proposed (see Patent Document 1). However, the microporous membrane has insufficient heat shrinkage resistance, and further improvement has been demanded.

JP 2004-149637 A

  Therefore, the problem to be solved by the present invention is to use a polyolefin and a high melting point thermoplastic resin to produce a microporous membrane excellent in heat shrinkage resistance, particularly a microporous membrane for a non-aqueous electrolyte secondary battery separator and production thereof. The object is to provide a method and a resin composition for a non-aqueous electrolyte secondary battery separator.

  As a result of diligent efforts to solve the above problems, the present inventors have found that a microporous film having a high melting point thermoplastic resin having a needle-like structure is excellent in heat shrinkage, and has completed the present invention. It was.

  That is, the present invention is a microporous film comprising a thermoplastic resin (a) having a melting point of 220 ° C. or higher and a polyolefin, wherein the thermoplastic resin (a) has a needle-like structure. About.

  The present invention also relates to a battery separator comprising the microporous membrane described above.

  In the present invention, the thermoplastic resin (a) having a melting point of 220 ° C. or higher and the polyolefin (b) are melt-kneaded at a temperature not lower than the melting point of the thermoplastic resin (a) to obtain a resin composition (α). Step (1) of obtaining, melt-kneading the obtained resin composition (α) and the pore-forming agent (d1) or β-crystal nucleating agent (d2) at a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher. Then, the step (2) of obtaining the melt-kneaded product (β), the melt-kneaded product (β) heated to a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or more is formed into a sheet, and heat having a needle-like structure The present invention relates to a method for producing a microporous membrane comprising a step (3) of obtaining a sheet (γ) containing a plastic resin (a) and a step (4) of making the obtained sheet (γ) porous.

  In the present invention, the thermoplastic resin (a) having a melting point of 220 ° C. or higher and the polyolefin (b) are melted at a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher in an extruder having a die attached to the tip. After kneading, the strand is formed so that the die hole diameter / strand diameter is 1.1 or more, and then the strand is cut, and the resin composition (α ′) containing the thermoplastic resin (a) having a needle-like structure is cut. The resin composition (α ′) and the pore-forming agent (d1) or β crystal nucleating agent (d2) obtained at a temperature not lower than the melting point of the polyolefin (b) and the thermoplasticity are obtained. Kneading at a temperature not higher than the melting point of the resin (a) to obtain a kneaded product (β ′) (2 ′), a temperature not lower than the melting point of the polyolefin (b) and not higher than the melting point of the thermoplastic resin (a). The melt-kneaded product (β ′) heated to a temperature is formed into a sheet and the needle A microporous material comprising: a step (3 ′) for obtaining a sheet (γ) containing a thermoplastic resin (a) having a shape structure; and a step (4) for making the obtained sheet (γ) porous. The present invention relates to a film manufacturing method.

  In the present invention, the thermoplastic resin (a) having a melting point of 220 ° C. or higher and the polyolefin (b) are melted at a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher in an extruder having a die attached to the tip. After kneading, forming a strand while taking the die hole diameter / strand diameter to be 1.1 or more, and then cutting the resin composition for a non-aqueous electrolyte secondary battery separator (α ′), The thermoplastic resin (a) is in the range of 1 to 73% by mass and the polyolefin (b) is in the range of 99 to 27% by mass with respect to the total mass (a + b) of the thermoplastic resin (a) and the polyolefin (b). Further, the present invention relates to a resin composition for a non-aqueous electrolyte secondary battery separator, wherein the thermoplastic resin (a) has a needle-like structure.

  According to the present invention, using a polyolefin and a high melting point thermoplastic resin, a microporous membrane excellent in heat shrinkage resistance, particularly a microporous membrane for a nonaqueous electrolyte secondary battery separator, a method for producing the same, and a nonaqueous electrolyte A resin composition for a secondary battery separator can be provided.

1 is a photomicrograph of the sheet specimen obtained in Example 4. FIG. It has a structure in which needle-shaped polyphenylene sulfide resin is dispersed in a polyolefin matrix. The white network structure is a polyolefin formed when the test piece is cut for SEM photography. FIG. 2 is a photomicrograph of the sheet test piece obtained in Comparative Example 1. It has a structure in which a spherical polyphenylene sulfide resin is dispersed in a polyolefin matrix. The white network structure is a polyolefin formed when the test piece is cut for SEM photography.

  The microporous membrane of the present invention is a microporous membrane containing a thermoplastic resin having a melting point of 220 ° C. or higher and a polyolefin, and the thermoplastic resin has a needle-like structure.

Thermoplastic resin having a melting point of 220 ° C. or higher As the thermoplastic resin used in the present invention, a thermoplastic resin such as a so-called general-purpose engineering plastic or super engineering plastic having a melting point of 220 ° C. or higher, preferably in the range of 220 to 390 ° C. Specifically, polyamide having an aliphatic skeleton such as polyamide 6 (6-nylon), polyamide 66 (6,6-nylon) or polyamide 12 (12-nylon), polyamide 6T (6T-nylon, polyamide) Polyamide having an aromatic skeleton such as 9T (9T-nylon) such as polyamide having a melting point of 220 ° C. or higher, preferably 220 to 310 ° C., polybutylene terephthalate, polyisobutylene terephthalate, polyethylene terephthalate or polycyclohex Polyester resin having a melting point such as terephthalate of 220 ° C. or higher, preferably 220 to 280 ° C., or polyphenylene having a melting point of 265 ° C. or higher, preferably 265 to 350 ° C., more preferably 280 to 300 ° C. Polyarylene sulfide typified by sulfide, polyether ether ketone having a melting point in the range of 300 to 390 ° C, melting point having parahydroxybenzoic acid in the skeleton is 300 ° C or higher, preferably 300 ° C to thermal decomposition temperature ( 380 ° C.) and a thermoplastic resin having a melting point of 220 to 390 ° C., such as syndiotactic polystyrene having a melting point of 220 or more, preferably 220 to 280 ° C. Polyarylene sulfides with excellent flame retardancy and dimensional stability are preferred That's right.

  In the present invention, the molecular weight of the thermoplastic resin is not particularly limited as long as the effects of the present invention are not impaired, but from the point of being able to suppress gasification and bleeding out of the resin component during melt kneading, As the value converted to, it is preferably in the range of 5 [Pa · s] or more, while the upper limit of the melt viscosity is not particularly problematic, but is in the range of 3000 [Pa · s] or less from the viewpoint of fluidity and moldability. It is preferable that it is in the range of 20 to 1000 [Pa · s]. The "melt viscosity" is a load of 1.96 MPa, an orifice length and an orifice using a flow tester (Shimadzu Koka flow tester "CFT-500D type") at the melting point of the thermoplastic resin plus 20 ° C. It shall refer to the melt viscosity after holding for 6 minutes using an orifice with a former / latter ratio of 10/1 to diameter. The “melting point” refers to the melting peak temperature measured by differential scanning calorimetry (DSC) in accordance with the method of JIS 7121 (1999) 9.1 (1).

  Here, the polyarylene sulfide resin mentioned as a preferable thermoplastic resin will be described in more detail.

  The polyarylene sulfide resin used in the present invention has a resin structure having a repeating unit of a structure in which an aromatic ring and a sulfur atom are bonded. Specifically, the polyarylene sulfide resin has the following formula (1):

（式中、Ｒ^１及びＲ^２は、それぞれ独立して水素原子、炭素原子数１〜４のアルキル基、ニトロ基、アミノ基、フェニル基、メトキシ基、エトキシ基を表す。）で表される構造部位を繰り返し単位とする樹脂である。

(Wherein, R ¹ and R ² each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a nitro group, an amino group, a phenyl group, a methoxy group, or an ethoxy group). It is a resin having a structural site as a repeating unit.

Here, in the structural site represented by the formula (1), R ¹ and R ² in the formula are preferably hydrogen atoms from the viewpoint of the mechanical strength of the polyarylene sulfide resin. A compound bonded at the para position represented by the following formula (2) is preferable.

これらの中でも、特に繰り返し単位中の芳香族環に対する硫黄原子の結合は前記構造式（２）で表されるパラ位で結合した構造であることが前記ポリアリーレンスルフィド樹脂の耐熱性や結晶性の面で好ましい。

Among these, in particular, the bond of the sulfur atom to the aromatic ring in the repeating unit is a structure bonded at the para position represented by the structural formula (2). In terms of surface.

  Further, the polyarylene sulfide resin is not only the structural portion represented by the formula (1), but also the following structural formulas (3) to (6).

で表される構造部位を、前記式（１）で表される構造部位との合計の３０モル％以下で含んでいてもよい。特に本発明では上記式（３）〜（６）で表される構造部位は１０モル％以下であることが、ポリアリーレンスルフィド樹脂の耐熱性、機械的強度の点から好ましい。前記ポリアリーレンスルフィド樹脂中に、上記式（３）〜（６）で表される構造部位を含む場合、それらの結合様式としては、ランダム共重合体、ブロック共重合体の何れであってもよい。

The structural site represented by the formula (1) may be included in an amount of 30 mol% or less in total. In particular, in the present invention, the structural portion represented by the above formulas (3) to (6) is preferably 10 mol% or less from the viewpoint of heat resistance and mechanical strength of the polyarylene sulfide resin. In the case where the polyarylene sulfide resin contains a structural portion represented by the above formulas (3) to (6), the bonding mode thereof may be either a random copolymer or a block copolymer. .

  The polyarylene sulfide resin has the following formula (7) in its molecular structure.

で表される３官能性の構造部位、或いは、ナフチルスルフィド結合などを有していてもよいが、他の構造部位との合計モル数に対して、３モル％以下が好ましく、特に１モル％以下であることが好ましい。

May have a trifunctional structural site represented by the formula (1) or a naphthyl sulfide bond, but is preferably 3 mol% or less, particularly 1 mol%, based on the total number of moles with other structural sites. The following is preferable.

  The polyarylene sulfide resin is not particularly limited as long as the effects of the present invention are not impaired, but the melt viscosity (V6) measured at 300 ° C. is preferably in the range of 5 to 3,000 [Pa · s], Furthermore, since the balance of fluidity | liquidity and mechanical strength becomes favorable, the range of 20-1000 [Pa * s] is more preferable. In addition, the non-Newtonian index of the polyarylene sulfide resin is not particularly limited as long as the effect of the present invention is not impaired, but is preferably in the range of 0.90 to 2.00. When the linear polyarylene sulfide resin is used, the non-Newtonian index is preferably in the range of 0.90 to 1.20, more preferably in the range of 0.95 to 1.15, particularly 0. Particularly preferred is .95 to 1.10. Such a polyarylene sulfide resin is excellent in mechanical properties, fluidity, and abrasion resistance. However, the non-Newtonian index (N value) is measured by measuring the shear rate and shear stress using a capillograph at 300 ° C, the ratio of the orifice length (L) to the orifice diameter (D), and L / D = 40. These are values calculated using the following formula.

［ただし、ＳＲは剪断速度（秒^−１）、ＳＳは剪断応力（ダイン／ｃｍ^２）、そしてＫは定数を示す。］Ｎ値は１に近いほどＰＰＳは線状に近い構造であり、Ｎ値が高いほど分岐が進んだ構造であることを示す。

[Wherein SR represents a shear rate (second ⁻¹ ), SS represents a shear stress (dyne / cm ² ), and K represents a constant. The closer the N value is to 1, the closer the PPS is to a linear structure, and the higher the N value is, the more branched the structure is.

  The method for producing the polyarylene sulfide resin is not particularly limited. For example, 1) a method in which a dihalogenoaromatic compound and, if necessary, other copolymerization components are polymerized in the presence of sulfur and sodium carbonate, 2) Method of self-condensing p-chlorothiophenol and further other copolymerization components if necessary, 3) In an organic polar solvent, sulfidizing agent and dihalogenoaromatic compound, and if necessary, other copolymerization components 4) a method in which a diiodo aromatic compound, elemental sulfur and, if necessary, a polymerization inhibitor are melt-polymerized in the presence of a polymerization catalyst. Among these methods, the method 3) is versatile and preferable. In the reaction, an alkali metal salt of carboxylic acid or sulfonic acid or an alkali hydroxide may be added to adjust the degree of polymerization. Among the above methods 3), a hydrous sulfiding agent is introduced into a mixture containing a heated organic polar solvent and a dihalogenoaromatic compound at a rate at which water can be removed from the reaction mixture, and the dihalogenoaromatic compound and A method for producing a PAS resin by reacting with a sulfidizing agent and controlling the amount of water in the reaction system in the range of 0.02 to 0.5 mol relative to 1 mol of the organic polar solvent No. 07-228699) and a polyhaloaromatic compound, an alkali metal hydrosulfide and an organic acid alkali metal salt in 1 mol of a sulfur source in the presence of a solid alkali metal sulfide and an aprotic polar organic solvent. 0.01 to 0.9 mol of organic acid alkali metal salt and the amount of water in the reaction system in the range of 0.02 mol with respect to 1 mol of aprotic polar organic solvent Those obtained in the control while a process of reacting (WO2010 / 058713 pamphlet reference.) Is particularly preferred.

  In the microporous membrane of the present invention, the thermoplastic resin has a needle-like structure and can impart more excellent heat shrinkage resistance to the microporous membrane, so that the aspect ratio is particularly in the range of 1.1 to 100. It is preferable that it is in the range of 1.5 to 50, more preferably in the range of 2 to 30. Furthermore, the thermoplastic resin having a needle-like structure not only has excellent heat shrinkage resistance, but also has good dispersibility of the thermoplastic resin in the resin composition. The length is preferably in the range of 10 to 5000 nm, more preferably in the range of 50 to 2000 nm, and even more preferably in the range of 80 to 500 nm.

  In addition, since the structure of the thermoplastic resin in the present invention is based on the image analysis result of the scanning electron micrograph, actually, not only the needle-like structure but also the plate-like structure or the rod-like structure In the present invention, these are also included in the needle-like structure.

Polyolefin The polyolefin used in the microporous membrane of the present invention is not limited in its type. For example, a homopolymer or copolymer obtained by polymerizing monomers such as ethylene, propylene, butene, methylpentene, hexene, and octene as raw materials. For example, two or more different homopolymers, copolymers, or multistage polymers may be mixed and used.

For example, when polyethylene is used as the polyolefin, the mass average molecular weight is preferably in the range of 5 × 10 ⁵ or more and 15 × 10 ⁶ or less. Examples of polyethylene include ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene. Of these, ultra high molecular weight polyethylene is preferred. The mass average molecular weight of the ultrahigh molecular weight polyethylene is preferably 1 × 10 ⁶ to 15 × 10 ⁶ , and more preferably 1 × 10 ^{6 to} 5 × 10 ⁶ . By making the mass average molecular weight 15 × 10 ⁶ or less, melt extrusion can be facilitated. Further, polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more, polyethylene having a weight average molecular weight of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , polypropylene having a weight average molecular weight of 1 × 10 ⁴ to 4 × 10 ⁶ , and a weight average molecular weight. 1 × ¹⁰ 4 ~4 × ^{10 6} of the polybutene-1, weight-average molecular weight 1 × 10 ³ or more to 1 × 10 ⁴ less than a polyethylene wax, and the mass average molecular weight 1 × ¹⁰ 4 ~4 × ^{10 6} ethylene · alpha- It is also preferable to mix at least one selected from the group consisting of olefin copolymers.

When polypropylene is used as the polyolefin, the mass average molecular weight is not particularly limited, but is preferably in the range of 1 × 10 ⁴ to 4 × 10 ⁶ .

When an ethylene / α-olefin copolymer is used together with a polyolefin, particularly a polyethylene having a mass average molecular weight of 5 × 10 ⁵ or more, the α-olefin may be propylene, butene-1, hexene-1, pentene-1, 4- Methyl pentene-1, octene, vinyl acetate, methyl methacrylate, styrene and the like are suitable.

  Among these, as the polyolefin (b) used in the present invention, high-density polyethylene, ultrahigh molecular weight polyethylene, or polypropylene is preferable. Further, when the microporous film is produced using the pore-forming agent (d1), the density is high. Polyethylene is more preferable, and polypropylene is more preferable when the microporous membrane is produced using the β crystal nucleating agent (d2).

  In the microporous membrane of the present invention, the composition ratio of the thermoplastic resin and the polyolefin is not particularly limited as long as the effects of the present invention are not impaired, but the thermoplastic resin is based on the total mass of the thermoplastic resin and the polyolefin. Is in the range of 1 to 73% by mass, and the polyolefin is preferably in the range of 99 to 27% by mass, the thermoplastic resin is in the range of 10 to 60% by mass, and the polyolefin is in the range of 90 to 40% by mass. A range is more preferable. Within this range, the dispersibility of the thermoplastic resin with respect to the polyolefin becomes good.

-Compatibilizer This invention can use a compatibilizer as needed, and can improve the compatibility of polyolefin and a thermoplastic resin by this, and is preferable. As the compatibilizing agent, a thermoplastic elastomer having a functional group having reactivity with the end of the thermoplastic resin is preferable. Further, a thermoplastic elastomer having a melting point of 300 ° C. or lower and having rubber elasticity at room temperature is more preferable. Among them, a thermoplastic elastomer having a glass transition point of −40 ° C. or less is preferable in view of heat resistance and ease of mixing because it has rubber elasticity even at low temperatures. Although the glass transition point tends to be preferable as it is low, the glass transition point is usually preferably in the range of -180 to -40 ° C, particularly preferably in the range of -150 to -40 ° C.

  Specific examples of the thermoplastic elastomer used in the present invention include at least one selected from the group consisting of epoxy groups, amino groups, hydroxy groups, carboxyl groups, mercapto groups, isocyanate groups, vinyl groups, acid anhydride groups, and ester groups. A thermoplastic elastomer having various functional groups is preferred, and among these, those having a functional group derived from a carboxylic acid derivative such as an epoxy group, an acid anhydride group, a carboxyl group, or an ester group are particularly preferred. The thermoplastic elastomer having these functional groups can be suitably used, particularly when a polyarylene sulfide resin is used as the thermoplastic resin, since the affinity between the thermoplastic resin and the polyolefin becomes good.

  The thermoplastic elastomer used in the present invention is obtained by copolymerizing one or more kinds of α-olefins and a vinyl polymerizable compound having the functional group. Examples of the α-olefins include α-olefins having 2 to 8 carbon atoms such as ethylene, propylene, and butene-1. Examples of the vinyl polymerizable compound having a functional group include α, β-unsaturated carboxylic acids such as (meth) acrylic acid and (meth) acrylic acid esters and alkyl esters thereof, maleic acid, fumaric acid, and itaconic acid. Other unsaturated dicarboxylic acids having 4 to 10 carbon atoms and mono- and diesters thereof, α, β-unsaturated dicarboxylic acids such as acid anhydrides and derivatives thereof, glycidyl (meth) acrylate, and the like.

  Among these, ethylene having at least one functional group selected from the group consisting of an epoxy group, amino group, hydroxy group, carboxyl group, mercapto group, isocyanate group, vinyl group, acid anhydride group and ester group in the molecule. -A propylene copolymer or an ethylene-butene copolymer is preferable, and an ethylene-propylene copolymer or an ethylene-butene copolymer having a carboxyl group is more preferable. These thermoplastic elastomers (c1) can be used alone or in combination of two or more.

  In the present invention, when a compatibilizing agent is used, the composition ratio of the thermoplastic resin, the polyolefin and the compatibilizing agent is not particularly limited as long as the effects of the present invention are not impaired, but the thermoplastic resin and the polyolefin are compatibilized. It is preferable that the total mass of the thermoplastic resin and the polyolefin is in the range of 97 to 90% by mass and the compatibilizer is in the range of 3 to 10% by mass with respect to the total mass with the agent. For example, even when the thermoplastic resin is contained in the polyolefin in a high concentration (for example, 40 to 73% by mass), the compatibility and dispersibility of the thermoplastic resin with respect to the polyolefin are preferable.

  Further, as long as the effects of the present invention are not impaired, known and commonly used lubricants, antiblocking agents, antistatic agents, antioxidants, light stabilizers, fillers, etc., in addition to the thermoplastic resin, polyolefin, and compatibilizer. Additives can be appropriately blended. In particular, since the microporous membrane of the present invention is melt-kneaded at a melting point or higher of the thermoplastic resin in the production process, an antioxidant is added in an amount of 0.01 to 5 masses per 100 mass parts of the polyolefin to prevent seizure of the polyolefin. It is preferable to add in the range of parts.

The microporous membrane of the present invention is, for example,
(Production Method 1) Thermoplastic resin having a melting point of 220 ° C. or higher (hereinafter referred to as a thermoplastic resin (a) having a melting point of 220 ° C. or higher in Production Method 1 and Production Method 2) and polyolefin (hereinafter referred to as Polyolefin (in Production Method 1 and Production Method 2) b)) is melt kneaded at a temperature equal to or higher than the melting point of the thermoplastic resin (a) in an extruder having a die attached to the tip, and a resin composition (hereinafter referred to as resin composition (α) in production method 1). The step (1) to obtain the resin composition (α) and the pore-forming agent (d1) or β-crystal nucleating agent (d2) obtained at a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher. Step (2) for obtaining a melt-kneaded product (β) by melt-kneading, a sheet of the melt-kneaded product (β) having a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or more, and heat having a needle-like structure Process for obtaining a sheet (γ) containing a plastic resin (a) (3), the obtained sheet (gamma) a porous to step (4), by the method for producing a microporous membrane having, or,
(Production Method 2) Melting and kneading thermoplastic resin (a) having a melting point of 220 ° C. or higher and polyolefin (b) at a temperature of melting point of thermoplastic resin (a) + 10 ° C. or higher in an extruder having a die attached to the tip. Then, after forming the strand while taking up the die hole diameter / strand diameter to be 1.1 or more, the resin composition containing the thermoplastic resin (a) having a needle-like structure after cutting (hereinafter referred to as resin in production method 2) Step (1 ′) for obtaining a composition (α ′)), and the resulting resin composition (α ′) and the pore-forming agent (d1) or β-crystal nucleating agent (d2) of the polyolefin (b) Kneading at a temperature not lower than the melting point and not higher than the melting point of the thermoplastic resin (a) to obtain a kneaded product (hereinafter referred to as kneaded product (β ′) in production method 2), the polyolefin ( a temperature equal to or higher than the melting point of b) and the thermoplastic resin ( ) To obtain a sheet (γ) containing the thermoplastic resin (a) having a needle-like structure by forming a kneaded product (β ′) having a temperature equal to or lower than the melting point of ()), and obtaining the obtained sheet (γ). It is obtained by the manufacturing method of the microporous film | membrane which has the process (4) made porous.

(Production method 1)
Process (1)
In the present invention, a thermoplastic resin (a) having a melting point of 220 ° C. or higher and a polyolefin (b) are melt-kneaded at a temperature not lower than the melting point of the thermoplastic resin (a) to obtain a resin composition (α). Step (1) is included.

  In the step (1), the thermoplastic resin (a) and the polyolefin (b) need to be uniformly dispersed with other blending components as necessary, so that the melting point of the thermoplastic resin + 10 ° C. As described above, it is more preferable to perform melt kneading under a temperature condition in which the set temperature is in the range of melting point + 10 ° C. to melting point + 100 ° C., more preferably in the range of melting point +20 to melting point + 50 ° C.

  In the step (1), an apparatus used for melt kneading is not particularly limited, but it is preferably performed in an extruder having a die attached to the tip. In the melt-kneading, the ratio (discharge amount / screw rotation number) between the discharge amount (kg / hr) of the blended component and the screw rotation speed (rpm) is 0.02 to 2.0 (kg / hr / rpm). It is carried out under conditions that are in the range, preferably in the range of 0.05 to 0.8 (kg / hr / rpm), more preferably in the range of 0.07 to 0.2 (kg / hr / rpm). Thereby, the morphology of the sea-island structure in which the thermoplastic resin (a) is uniformly finely dispersed using the polyolefin (b) as a matrix can be formed, and as a result, the film thickness in the sheeting process becomes uniform.

  In the step (1), the resin composition (α) discharged from the die after melt kneading is a pellet, powder, plate, fiber, strand, film or sheet, pipe, Although it can be formed into a hollow shape, box shape, etc., it is in the form of pellets from the viewpoint of handleability such as storage and transportation, and from the point that it can be easily uniformly dispersed during kneading in step (2). Preferably there is.

  In the step (1), the charging ratio of the thermoplastic resin (a) and the polyolefin (b) is the thermoplastic resin with respect to the total mass (a + b) of the thermoplastic resin (a) and the polyolefin (b). It is preferable that (a) is in the range of 1 to 73% by mass and polyolefin (b) is in the range of 99 to 27% by mass, and further, the thermoplastic resin (a) is in the range of 10 to 60% by mass. More preferably, the polyolefin (b) is in the range of 90 to 40% by mass. In the said range, since the dispersibility of the thermoplastic resin (a) with respect to polyolefin (b) becomes favorable, it is preferable.

  In the step (1), when the thermoplastic resin (a) and the polyolefin (b) are further added with a compatibilizer (c) and melt kneaded, the thermoplastic resin (a) and the polyolefin (b) The charging ratio with the compatibilizing agent (c) is such that the thermoplastic resin (a) and the polyolefin are the total mass (a + b + c) of the thermoplastic resin (a), the polyolefin (b) and the compatibilizing agent (c). It is preferable that the total mass (a + b) of (b) is in the range of 97 to 90% by mass and the compatibilizer (c) is in the range of 3 to 10% by mass. If it is the said range, even if it is a case where thermoplastic resin (a) is contained in polyolefin (b) by high concentration (for example, 40-73 mass%), thermoplastic resin (a) with respect to polyolefin (b) This is preferable because the compatibility and dispersibility of the resin are good.

  In addition, in the step (1), as other blending components, a lubricant, an antiblocking agent, an antistatic agent, an antioxidant, in addition to the above components (a) to (c), as long as the effects of the present invention are not impaired. Known and commonly used additives such as light stabilizers and fillers can be appropriately blended. In particular, in the step (1), since the melt kneading is performed at a temperature equal to or higher than the melting point of the thermoplastic resin (a), an antioxidant is added in an amount of 0.01 to 5 masses per 100 mass parts of the polyolefin (b) in order to prevent seizure of the polyolefin. It is preferable to add in the range of parts.

Step (2)
In the present invention, the obtained resin composition (α) and the pore-forming agent (d1) or β-crystal nucleating agent (d2) are melt-kneaded at a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or more, A step (2) of obtaining a melt-kneaded product (β).

・ Pore forming agent (d1)
As the pore-forming agent (d1), a known and commonly used one can be used, but it is particularly limited as long as it dissolves in the solvent used in the step (4) for making the sheet (γ) described later porous. For example, calcium carbonate fine particles are preferable, but inorganic fine particles such as magnesium sulfate fine particles, calcium oxide fine particles, calcium hydroxide fine particles, silica fine particles, and a solid or liquid solvent at room temperature may be used. it can.

  Solvents that are liquid at room temperature include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, liquid paraffin, and mineral oil fractions with boiling points corresponding to these, and dibutyl phthalate, dioctyl Examples of the phthalate are liquid phthalates at room temperature, and it is preferable to use a non-volatile liquid solvent such as liquid paraffin.

  The solvent that is solid at room temperature is in a state of being mixed with polyolefin in the heated melt-kneaded state, but may be a solid solvent at room temperature, and stearyl alcohol, seryl alcohol, paraffin wax and the like can be used. If only a solid solvent is used, stretching unevenness or the like may occur, so it is preferable to use a liquid solvent in combination.

  In the step (2), when the hole forming agent (d1) is used, the charging ratio between the resin composition (α) and the hole forming agent (d1) is such that the resin composition (α) and the hole forming agent (d1) are used. ) And the total mass (α + d1) of the resin composition (α) is preferably in the range of 30-80% by mass, and the pore-forming agent (d1) is preferably in the range of 70-20% by mass. More preferably, the resin composition (α) is in the range of 50 to 70% by mass and the pore-forming agent (d1) is in the range of 50 to 30% by mass.

  The hole forming agent (d1) may be added before the start of the melt kneading in step (2), or may be added from the middle of the extruder during the melt kneading. Is preferred. In melt kneading, an antioxidant is preferably added to prevent oxidation of the polyolefin.

.Beta. Crystal nucleating agent (d2)
Examples of the β crystal nucleating agent used in the present invention include those shown below, but are not particularly limited as long as they increase the production / growth of β crystals of the polypropylene-based resin, and two or more types are also included. You may mix and use.

  Examples of the β crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by, etc .; binary compounds composed of organic dibasic acids and Group IIA metal oxides, hydroxides or salts of periodic table; compositions composed of cyclic phosphorus compounds and magnesium compounds, etc. Can be mentioned. Commercially available products of such β crystal nucleating agents include β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., and specific examples of polypropylene resins to which β crystal nucleating agents are added include polypropylene manufactured by Aristech. Examples include “Bepol B-022SP”, Borealis polypropylene “Beta (β) -PP BE60-7032”, Mayzo polypropylene “BNX BETAPP-LN”, and the like.

  When the β crystal nucleating agent (d2) is used in the step (2), the charging ratio of the β crystal nucleating agent (d2) in the resin composition (α) is not particularly limited as long as the effects of the present invention are not impaired. However, considering the strength and toughness of the sheet or porous membrane, it is preferably in the range of 0.0001 to 10 parts by mass with respect to 100 parts by mass of the polyolefin (b) in the resin composition (α). Furthermore, the range of 0.001-5 mass parts is more preferable, and the range of 0.01-1 mass part is the most preferable. If it is 0.0001 part by mass or more, β crystals can be generated and grown, and sufficient β activity can be secured even when used as a separator, and the desired air permeation performance is obtained. If it is at most parts, bleeding of the β crystal nucleating agent can be suppressed, which is preferable.

・ Polyolefin (e)
In step (2), polyolefin (hereinafter referred to as polyolefin (e)) can be further blended and diluted with respect to the resin composition (α) obtained in step (1). There is no limitation in the kind as polyolefin (e), The thing similar to the said polyolefin (b) can be used.

  In the step (2), when the polyolefin (e) is used, the charging ratio is determined between the thermoplastic resin (a), the polyolefin (b), and the polyolefin (e) contained in the resin composition (α). The thermoplastic resin (a) is in the range of 1 to 73% by mass relative to the total mass (a + b + e), and the total mass (b + e) of the polyolefin (b) and the polyolefin (e) is in the range of 99 to 27 parts by mass. It is preferable that the thermoplastic resin (a) is in the range of 5 to 60% by mass, the total mass (b + e) is more preferably in the range of 95 to 40% by mass, and the thermoplastic resin (a). More preferably, the total mass (b + e) is in the range of 80 to 60% by mass with respect to 20 to 40% by mass.

  Further, in the step (2), a lubricant, an anti-blocking agent, an antistatic agent, in addition to the components (α), (d1) or (d2), and (e), as long as the effects of the present invention are not impaired. Known and commonly used additives such as antioxidants, light stabilizers, crystal nucleus materials, fillers and the like can be appropriately blended.

  In the step (2), the melting and kneading temperature is the melting point of the thermoplastic resin + 10 ° C. or more, more preferably the set temperature is in the range of melting point + 10 to melting point + 100 ° C., more preferably in the range of melting point + 20 to melting point + 50 ° C.

  In the step (2), the method of melt kneading is not particularly limited, but it is preferably performed by uniformly kneading in an extruder, and since the subsequent step (3) can be continuously performed, More preferably, it is carried out in an extruder equipped with a sheet die such as a T die.

  In the melt-kneading in the step (2), the ratio (discharge amount / screw rotation number) between the discharge amount (kg / hr) of the blended component and the screw rotation number (rpm) is preferably 0.02 to 2.0 ( kg / hr / rpm), more preferably 0.05 to 0.8 (kg / hr / rpm), and even more preferably 0.07 to 0.2 (kg / hr / rpm). Perform under conditions. Thus, when the thermoplastic resin (a) is added using the polyolefin (b) and the polyolefin (e) as a matrix, and the pore-forming agent (d1) or the β-crystal nucleating agent (d2) is further added, the pore-forming agent (d1 ) Or β-crystal nucleating agent (d2) can be uniformly dispersed in a sea-island structure, resulting in not only uniform film thickness in the sheeting process, but also uniform pore distribution and A microporous film having a fine pore diameter can be formed.

  In the step (2), after the melt-kneading, the melt-kneaded product (β) is shaped into pellets, powders, plates, fibers, strands, films or sheets, pipes, hollows, boxes, etc. It can be cooled and pelletized once, such as by molding, but from the viewpoint of productivity, it can be melted and kneaded using an extruder with a T die attached to the tip, directly or via another extruder It is preferable to continuously perform the following step (3).

Step (3)
The present invention includes a step (3) of obtaining a sheet (γ) by forming a sheet of the melt-kneaded product (β) heated to the melting point of the thermoplastic resin (a) + 10 ° C. or more.

  In step (3), the melt-kneaded product (β) is once cooled and pelletized, and then extruded again from the die through an extruder, directly or through another extruder, and cast roll. Alternatively, it is preferable to take a roll such as a roll take-up machine so that the gap (lip width) / sheet thickness of the lip part of the die is in the range of 1.1 to 40, and further in the range of 2 to 20. More preferred. As the die, a sheet die having a rectangular base shape is preferably used, but a double cylindrical hollow die, an inflation die, or the like can also be used. In the case of a sheet die, the gap (lip width) of the lip portion of the die is usually preferably 0.1 to 5 mm, and at the time of extrusion, this is more preferably the temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or more. Heats the set temperature to a temperature in the range of melting point +10 to melting point + 100 ° C., more preferably in the range of melting point +20 to 50 ° C. The extrusion rate of the heated solution is preferably in the range of 0.2 to 50 (m / min).

  The sheet (γ) is formed by cooling the melt-kneaded product (β) thus extruded from the die. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature or less. Moreover, it is preferable to cool to 25 degrees C or less. Thus, while the phase which consists of polyolefin gelatinizes, the phase-separated structure where the thermoplastic resin (a) was disperse | distributed to the polyolefin phase can be fixed. When the cooling rate is less than 50 ° C./min, the degree of crystallinity increases, and it tends to be difficult to obtain a sheet suitable for stretching. As a cooling method, a method of directly contacting cold air, cooling water, or other cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used. The draft ratio ((roll take-up speed) / (flow rate of resin flowing out from the die lip converted from the density)) is preferably 1 to 600 times, more preferably from the viewpoint of air permeability and moldability. 1 to 200 times, more preferably 1 to 100 times.

  In addition, in that case, when using a hole formation agent (d1), it is preferable to cool to 25 degrees C or less. On the other hand, when the β crystal nucleating agent (d2) is used, the β crystal ratio of the polyolefin (b) is adjusted in the range of 20 to 100%, preferably in the range of 50 to 100%. It is preferable to cool to 90 to 140 ° C. However, the β crystal ratio is determined by using a differential scanning calorimeter when the film-like material is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min. The ratio (%) calculated by [ΔHmβ / (ΔHmβ + ΔHmα)] × 100 (%) using the heat of crystal fusion derived from the α crystal (ΔHmα) and the heat of crystal fusion derived from the β crystal (ΔHmβ).

Process (4)
The present invention includes a step (4) of making the sheet (γ) obtained in the step (3) porous.

  The porosification step of the step (4) is roughly classified into a case where the pore forming agent (d1) is used and a case where the β crystal nucleating agent (d2) is used. First, the case where the hole forming agent (d1) is used will be described.

  In the case of using the pore-forming agent (d1), in the step (4), a microporous membrane called so-called wet method is formed in which the microporous material is formed by eluting the pore-forming agent (d1) using an acidic aqueous solution. A step (4a) of removing the hole-forming agent (d1) after stretching the sheet (γ), and after removing the hole-forming agent (d1) from the sheet (γ). Examples include a step (4b) of stretching, or a step (4c) of removing the hole forming agent (d1) after stretching the sheet (γ) and further stretching.

  In any of the methods of steps (4a) to (4c), stretching is performed at a predetermined magnification by heating the sheet (γ) and then using a normal tenter method, roll method, inflation method, rolling method, or a combination of these methods. Do. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, any of simultaneous biaxial stretching, sequential stretching or multistage stretching (combination of simultaneous biaxial stretching and sequential stretching) may be used, but sequential biaxial stretching is particularly preferable. The mechanical strength is improved by stretching.

  The stretching ratio varies depending on the thickness of the sheet (γ), but when uniaxial stretching is performed, the stretching ratio is preferably 2 times or more, and more preferably 3 to 30 times. In biaxial stretching, it is preferably at least 2 times in any direction, preferably 4 times or more in terms of surface magnification, and more preferably 6 times or more in terms of surface magnification. By setting the surface magnification to 4 times or more, the puncture strength can be improved. On the other hand, when the surface magnification is more than 100 times, restrictions tend to occur in terms of stretching devices, stretching operations, and the like.

  When the polyolefin is a homopolymer, the stretching temperature is preferably the melting point + 10 ° C. or less, and more preferably within the range from the crystal dispersion temperature to less than the crystal melting point. When the stretching temperature exceeds the melting point + 10 ° C., the polyolefin is melted and the molecular chain cannot be oriented by stretching. Further, when the stretching temperature is lower than the crystal dispersion temperature, the polyolefin is not sufficiently softened, the film is easily broken during stretching, and high-stretching cannot be performed. However, when performing sequential stretching or multistage stretching, primary stretching may be performed at a temperature lower than the crystal dispersion temperature. Here, the crystal dispersion temperature refers to a value obtained by measuring temperature characteristics of dynamic viscoelasticity based on ASTM D 4065. The crystal dispersion temperature of polyethylene is generally 90 ° C.

  When the polyolefin contains polyethylene, the stretching temperature is preferably in the range from the crystal dispersion temperature of the polyethylene to the crystal melting point + 10 ° C. or less. When polyethylene or a composition containing it is used as the polyolefin, in the present invention, the stretching temperature is usually preferably 100 to 130 ° C, more preferably 110 to 120 ° C.

  Depending on the desired physical properties, the film can be stretched by providing a temperature distribution in the film thickness direction, or can be subjected to sequential stretching or multi-stage stretching in which the film is first stretched at a relatively low temperature and then secondarily stretched at a higher temperature. By providing a temperature distribution in the film thickness direction and stretching, a microporous film generally excellent in mechanical strength can be obtained. As the method, for example, the method disclosed in JP-A-7-188440 can be applied.

  For removal of the pore-forming agent (d1), a solvent capable of dissolving the pore-forming agent (d1) (hereinafter referred to as a removal solvent) is used. By removing the pore-forming agent (d1) uniformly finely dispersed using the removal solvent, a porous film can be obtained. Specific examples of the removal solvent include, for example, acidic aqueous solutions such as hydrochloric acid, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, hydrocarbons such as pentane, hexane and heptane, fluorinated hydrocarbons such as ethane trifluoride, Examples include easily volatile solvents such as ethers such as diethyl ether and dioxane, and methyl ethyl ketone. As the removal solvent, in addition to the above, a solvent disclosed in JP-A No. 2002-256099 having a surface tension at 25 ° C. of 24 mN / m or less can be used. By using a solvent having such a surface tension, the shrinkage and densification of the network structure caused by the surface tension of the gas-liquid interface generated inside the microporous layer during drying after removing the pore-forming agent (d1) is suppressed. As a result, the porosity and permeability of the microporous membrane are further improved.

  The removal method of the pore-forming agent (d1) is based on a method of immersing the stretched film or sheet (γ) in a removal solvent, a method of showering the removal solvent on the stretched film or sheet (γ), or a combination thereof. It can be performed by a method or the like. The removal solvent is preferably used in an amount of 300 to 30000 parts by mass with respect to 100 parts by mass of the sheet (γ). The removal treatment with the removal solvent is preferably performed until the remaining pore-forming agent is less than 1% by mass with respect to the amount added.

  On the other hand, when the β crystal nucleating agent (d2) is used, the step (4) is a so-called dry process in which a microporous material is formed by stretching a sheet containing a polyolefin having β crystals, particularly preferably a polypropylene resin. This is a process for producing a microporous membrane called a method, and examples thereof include a process (4d) for stretching the sheet (γ).

  In the step (4d), the stretching is performed at a predetermined magnification by heating the sheet (γ) and then by a usual tenter method, roll method, inflation method, rolling method, or a combination of these methods. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, any of simultaneous biaxial stretching, sequential stretching or multistage stretching (combination of simultaneous biaxial stretching and sequential stretching) may be used, but sequential biaxial stretching is particularly preferable. The mechanical strength is improved by stretching.

The stretching ratio varies depending on the thickness of the sheet (γ), but when uniaxial stretching is performed, the stretching ratio is preferably 2 times or more, and more preferably 3 to 30 times. In biaxial stretching, it is preferably at least 2 times in any direction, preferably 4 times or more in terms of surface magnification, and more preferably 6 times or more in terms of surface magnification. By setting the surface magnification to 4 times or more, the puncture strength can be improved. On the other hand, when the surface magnification is more than 100 times, restrictions tend to occur in terms of stretching devices, stretching operations, and the like.
In the case of using the β crystal nucleating agent (d2), the stretching step may be uniaxial stretching in the longitudinal direction or the transverse direction, or may be biaxial stretching. Moreover, when performing biaxial stretching, simultaneous biaxial stretching may be sufficient and sequential biaxial stretching may be sufficient. When producing the polyolefin resin porous film of the present invention, sequential biaxial stretching is more preferable because the stretching conditions can be selected in each stretching step and the porous structure can be easily controlled.
When using sequential biaxial stretching, the stretching temperature needs to be changed from time to time depending on the composition of the resin composition to be used, the crystal melting peak temperature, the degree of crystallinity, etc., but the stretching temperature in the longitudinal stretching is preferably about 0 to 130 ° C. More preferably, it is controlled in the range of 10 to 120 ° C, and more preferably 20 to 110 ° C. The longitudinal draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times, still more preferably 4 to 7 times. By performing longitudinal stretching within the above range, it is possible to develop an appropriate pore starting point while suppressing breakage during stretching.

  On the other hand, the stretching temperature in transverse stretching is generally 100 to 160 ° C, preferably 110 to 150 ° C, and more preferably 120 to 140 ° C. Moreover, a preferable lateral stretch ratio is 2 to 10 times, more preferably 3 to 8 times, and still more preferably 4 to 7 times. By transversely stretching within the above range, the pore starting point formed by longitudinal stretching can be appropriately expanded, and a fine porous structure can be expressed.

  The stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 1500 to 10,000% / min, and further preferably 2500 to 8000% / min.

-Other processing process The film | membrane obtained through process (4) can give well-known post-processing processes, such as a drying process, heat processing, a crosslinking process, or a hydrophilization process.
Examples of the drying treatment include a method of drying by a heat drying method or an air drying method. The drying temperature is preferably a temperature not higher than the crystal dispersion temperature of polyolefin, and particularly preferably a temperature lower by 5 ° C. or more than the crystal dispersion temperature.

  By the drying treatment, the content of the removal solvent remaining in the microporous membrane is preferably 5% by mass or less (the membrane mass after drying is 100% by mass), and 3% by mass or less. More preferred. If the drying solvent is insufficient and a large amount of the removal solvent remains in the film, it is not preferable because the porosity is lowered and permeability is deteriorated by a subsequent heat treatment.

  In the present invention, it is preferable to perform a heat treatment as a post-treatment. The crystal is stabilized by the heat treatment, and the lamellar layer is made uniform. As the heat treatment method, any method of heat stretching treatment, heat setting treatment, or heat shrinkage treatment may be used, and these methods are appropriately selected according to the physical properties required for the microporous membrane. These heat treatments are preferably performed at a temperature not lower than the crystallization temperature of the polyolefin of the microporous membrane and not higher than the melting point, and more preferably performed at an intermediate temperature between the crystallization temperature and the melting point.

  The heat stretching treatment is performed by a commonly used tenter method, roll method, or rolling method, and is preferably performed in a range of a draw ratio of 1.01 to 2.0 times in at least one direction, and is 1.01 to 1.5 times. It is more preferable to carry out within a range.

  The heat setting treatment is performed by a tenter method, a roll method or a rolling method. Moreover, you may perform a heat shrink process by a tenter system, a roll system, or a rolling system, or may be performed using a belt conveyor or a floating. The heat shrinkage treatment is preferably performed in a range of 50% or less in at least one direction, and more preferably performed in a range of 30% or less.

  In addition, you may perform combining many above-mentioned heat | fever extending processes, heat setting processes, and heat shrink processes. In particular, when the heat stretching treatment is performed after the heat setting treatment, the permeability of the obtained microporous membrane is improved and the pore diameter is enlarged. Further, it is preferable to perform a heat shrinking treatment after the heat stretching treatment because a microporous membrane having a low shrinkage rate and a high strength can be obtained.

  Furthermore, as the cross-linking treatment, α-rays, β-rays, γ-rays, electron beams, etc. are used as ionizing radiation, and ionizing radiation is performed with an electron dose of 0.1 to 100 Mrad and an acceleration voltage of 100 to 300 kV. Can be crosslinked. Thereby, meltdown temperature can be improved.

  Moreover, as a hydrophilic treatment, a monomer graft, a surfactant treatment, a corona discharge treatment or the like can be performed to hydrophilize the microporous membrane. The monomer grafting treatment is preferably performed after ionizing radiation.

  When performing a surfactant treatment using a surfactant as a hydrophilic treatment, any of a nonionic surfactant, a cationic surfactant, an anionic surfactant or an amphoteric surfactant can be used. However, it is preferable to use a nonionic surfactant. In the case of using a surfactant, the surfactant is made into an aqueous solution or a solution of a lower alcohol such as methanol, ethanol, isopropyl alcohol, and dipped or hydrophilized by a method using a doctor blade. The microporous membrane that has been hydrophilized is then dried. At this time, in order to improve permeability, it is preferable to perform heat treatment while preventing shrinkage at a temperature below the melting point of the microporous membrane. Examples of the method of performing heat treatment while preventing shrinkage include a method of performing heat treatment while stretching.

  Furthermore, the microporous membrane of the present invention can be subjected to known surface treatments such as a corona treatment machine, a plasma treatment machine, an ozone treatment machine, and a flame treatment machine.

(Manufacturing method 2)
Process (1 ')
In the present invention, after melting and kneading the thermoplastic resin (a) having a melting point of 220 ° C. or more and the polyolefin (b) at a temperature not lower than the melting point of the thermoplastic resin (a) in an extruder having a die attached to the tip. (1) A step of forming a strand while taking the die hole diameter / strand diameter to be 1.1 or more and then cutting to obtain a resin composition (α ′) containing a thermoplastic resin (a) having a needle-like structure (1) '), Have.

  In the step (1 ′), it is necessary to uniformly disperse the thermoplastic resin (a) and the polyolefin (b) and, if necessary, other blending components, so that the melting point of the thermoplastic resin +10 It is preferable to perform melt-kneading under a temperature condition of a melting point + 10 to a melting point + 100 ° C., more preferably a melting point + 20 to a melting point + 50 ° C.

  In the step (1 '), the apparatus used for melt kneading is preferably performed in an extruder having a die attached to the tip. In the melt-kneading, the ratio (discharge amount / screw rotation number) between the discharge amount (kg / hr) of the blended component and the screw rotation speed (rpm) is preferably 0.02 to 2.0 (kg / hr / rpm), more preferably 0.05 to 0.8 (kg / hr / rpm), and even more preferably 0.07 to 0.2 (kg / hr / rpm). . Thereby, the morphology of the sea-island structure in which the thermoplastic resin (a) is uniformly finely dispersed using the polyolefin (b) as a matrix can be formed, and as a result, the film thickness in the sheeting process becomes uniform.

  In the step (1 ′), after melt-kneading, the die hole diameter / strand diameter is preferably in the range of 1.1 or more, more preferably in the range of 1.1 to 3, further preferably in the range of 1.5 to 2. After forming the strands while being taken, the strands are cut by a known method to form pellets, powders, plates, fibers, strands, films or sheets, pipes, hollows, boxes, etc. By molding, a resin composition (α ′) containing the thermoplastic resin (a) having a needle-like structure can be obtained. The shape is preferably in the form of pellets from the viewpoint of handling properties such as storage and transportation, and also from the viewpoint that it can be easily and uniformly dispersed during the kneading in the step (2 '). In the present invention, the die hole diameter refers to the diameter of the discharge nozzle of the die.

  In the step (1 ′), the charging ratio of the thermoplastic resin (a) to the polyolefin (b) is the thermoplasticity relative to the total mass (a + b) of the thermoplastic resin (a) and the polyolefin (b). The resin (a) is preferably in the range of 1 to 73% by mass, the polyolefin (b) is preferably in the range of 99 to 27% by mass, and the thermoplastic resin (a) is in the range of 10 to 60% by mass. More preferably, the polyolefin (b) is in the range of 90 to 40% by mass. In the said range, since the dispersibility of the thermoplastic resin (a) with respect to polyolefin (b) becomes favorable, it is preferable.

  In addition, in the step (1 ′), when the compatibilizer (c) is further added to the thermoplastic resin (a) and the polyolefin (b) and melt-kneaded, the charging ratio of the compatibilizer (c) is: With respect to the total mass (a + b + c) of the thermoplastic resin (a), polyolefin (b), and compatibilizer (c), the total mass (a + b) of the thermoplastic resin (a) and polyolefin (b) is 97 to 97 It is preferable that the range is 90% by mass and the compatibilizer (c) is in the range of 3 to 10% by mass. If it is the said range, even if it is a case where thermoplastic resin (a) is contained in polyolefin (b) by high concentration (for example, 40-73 mass%), thermoplastic resin (a) with respect to polyolefin (b) This is preferable because the compatibility and dispersibility of the resin are good.

  In addition, in the step (1 ′), as other blending components, a lubricant, an antiblocking agent, an antistatic agent, an antioxidant other than the above components (a) to (c), as long as the effects of the present invention are not impaired. In addition, known and conventional additives such as light stabilizers and fillers can be appropriately blended. In particular, in the step (1 ′), since the melt kneading is performed at a temperature equal to or higher than the melting point of the thermoplastic resin (a), an antioxidant is added in an amount of 0.01 to 5 parts per 100 parts by mass of the polyolefin (b) in order to prevent seizure of the polyolefin. It is preferable to add in the range of parts by mass.

Process (2 ')
In the present invention, the resin composition (α ′) obtained in the step (1 ′) and the pore-forming agent (d1) or the β crystal nucleating agent (d2) are heated to a temperature equal to or higher than the melting point of the polyolefin (b) and the heat. A step (2 ′) of obtaining a kneaded product (β ′) by kneading the molten polyolefin (b) and the thermoplastic resin (a) having a needle-like structure at a temperature below the melting point of the plastic resin (a); Have

-Hole formation agent As a hole formation agent (d1), the thing similar to what was used by the said manufacturing method 1 can be used.

  In the step (2 ′), when the hole forming agent (d1) is used, the charging ratio between the resin composition (α ′) and the hole forming agent (d1) is set so that the resin composition (α ′) and the hole forming agent are formed. The resin composition (α ′) is in the range of 30 to 80% by mass and the pore-forming agent (d1) is in the range of 70 to 20% by mass with respect to the total mass (α ′ + d1) with the agent (d1). It is preferable that the resin composition (α ′) is in the range of 50 to 70% by mass, and the pore forming agent (d1) is more preferably in the range of 50 to 30% by mass.

  The hole forming agent (d1) may be added before the start of kneading in the step (2 ′) or may be added from the middle of the extruder during the kneading, but it is added in advance before the kneading starts to form a solution. preferable. In kneading, it is preferable to add an antioxidant in order to prevent oxidation of the polyolefin.

.Beta. Crystal nucleating agent (d2)
As the β crystal nucleating agent used in the present invention, those similar to those used in the production method 1 can be used.

  When the β crystal nucleating agent (d2) is used in the step (2 ′), the charging ratio of the β crystal nucleating agent (d2) in the resin composition (α ′) is not particularly limited as long as the effects of the present invention are not impaired. Although it is not a thing, when the intensity | strength and toughness of a sheet | seat and a porous membrane are considered, it is the range of 0.0001-10 mass parts with respect to 100 mass parts of polyolefin (b) in a resin composition ((alpha) '). The range of 0.001 to 5 parts by mass is more preferable, and the range of 0.01 to 1 part by mass is most preferable. If it is 0.0001 part by mass or more, β crystals can be generated and grown, and sufficient β activity can be secured even when used as a separator, and the desired air permeation performance is obtained. If it is at most parts, bleeding of the β crystal nucleating agent can be suppressed, which is preferable.

・ Polyolefin (e)
In the step (2 ′), the polyolefin (e) can be further blended and diluted with the resin composition (α ′) obtained in the step (1 ′).

  In the step (2 ′), when the polyolefin (e) is used, the charging ratio is determined based on the thermoplastic resin (a), the polyolefin (b) and the polyolefin (e) contained in the resin composition (α ′). The thermoplastic resin (a) is in the range of 1 to 73% by mass and the total mass (b + e) of the polyolefin (b) and the polyolefin (e) is 99 to 27 parts by mass with respect to the total mass (a + b + e). The thermoplastic resin (a) is preferably in the range of 5 to 60% by mass, the total mass (b + e) is more preferably in the range of 95 to 40% by mass, and the thermoplastic resin ( It is more preferable that the total mass (b + e) is in the range of 80 to 60% by mass with respect to a) of 20 to 40% by mass.

  Further, in the step (2 ′), a lubricant, an anti-blocking agent, an antistatic agent, an antioxidant other than the above components (α ′), (d) and (e), as long as the effects of the present invention are not impaired. In addition, known and conventional additives such as a light stabilizer, a crystal nucleus material, and a filler can be appropriately blended.

  In the step (2 ′), the kneading temperature is not less than the melting point of the polyolefin (b) and not more than the melting point of the thermoplastic resin (a). The melting point of the polyolefin (b) plus 10 ° C. or higher and the melting point of the thermoplastic resin (a) minus 10 ° C. or lower are preferable. In addition, when the polyolefin (e) is blended, it may be higher than the melting point of the higher one of the polyolefin (b) and the polyolefin (e), but the higher of the polyolefin (b) and the polyolefin (e). The melting point of the thermoplastic resin (a) is preferably within the range of the melting point plus 10 ° C. or more and the melting point minus 10 ° C. or less.

  In the step (2 ′), the kneading method is not particularly limited, but it is preferably performed by uniformly kneading in an extruder, and further, since the subsequent step (3) can be continuously performed, More preferably, it is carried out in an extruder equipped with a sheet die such as a T die.

  In the kneading in the step (2 ′), the ratio (discharge amount / screw rotation number) between the discharge amount (kg / hr) and the screw rotation speed (rpm) of the blended component is preferably 0.02 to 2.0 ( kg / hr / rpm), more preferably 0.05 to 0.8 (kg / hr / rpm), and even more preferably 0.07 to 0.2 (kg / hr / rpm). Perform under conditions. Thus, when the thermoplastic resin (a) is added using the polyolefin (b) and the polyolefin (e) as a matrix, and the pore-forming agent (d1) or the β-crystal nucleating agent (d2) is further added, the pore-forming agent (d1 ) Or β-crystal nucleating agent (d2) can be uniformly dispersed in a sea-island structure, resulting in not only uniform film thickness in the sheeting process, but also uniform pore distribution and A microporous film having a fine pore diameter can be formed.

  In the step (2 ′), after melt-kneading, the melt-kneaded product (β ′) is in the form of pellets, powders, plates, fibers, strands, films or sheets, pipes, hollows, boxes, etc. It can be cooled into pellets once it has been molded into a shape, etc., but from the viewpoint of productivity, it can be melted and kneaded using an extruder with a T die attached to the tip, directly or by using another extruder. Therefore, it is preferable to continuously perform the subsequent step (3 ′).

Process (3 ')
The present invention provides a step (3 ′) of obtaining a sheet (γ) containing a thermoplastic resin (a) having a needle-like structure by forming a sheet of the kneaded product (β ′) heated to the melting point of the polyolefin (b) or higher. Have.

  After the melt-kneaded melt-kneaded product (β ′) is once cooled and pelletized, it is extruded from the die again through an extruder or directly or through another extruder, cast roll or roll take-up machine, etc. Take over with the roll. As the die, a sheet die having a rectangular base shape is preferably used, but a double cylindrical hollow die, an inflation die, or the like can also be used. In the case of a sheet die, the die gap is usually preferably 0.1 to 5 mm, and at the time of extrusion, the temperature is not lower than the melting point of the polyolefin (b) and not higher than the melting point of the thermoplastic resin (a), more preferably. It is preferable to carry out within the range of the melting point of the polyolefin (b) plus 10 ° C. or more and the melting point of the thermoplastic resin (a) minus 10 ° C. or less. In addition, when the polyolefin (e) is blended, it may be higher than the melting point of the higher one of the polyolefin (b) and the polyolefin (e), but the higher of the polyolefin (b) and the polyolefin (e). The melting point of the thermoplastic resin (a) is preferably within the range of the melting point plus 10 ° C. or more and the melting point minus 10 ° C. or less. Specifically, it is preferable to heat in the range of 140 to 250 ° C. The extrusion rate of the heated solution is preferably in the range of 0.2 to 15 (m / min).

  The sheet (γ) is formed by cooling the melt-kneaded product (β ′) thus extruded from the die. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature or less. Moreover, it is preferable to cool to 25 degrees C or less. Thus, while the phase which consists of polyolefin gelatinizes, the phase-separated structure where the thermoplastic resin (a) was disperse | distributed to the polyolefin phase can be fixed. When the cooling rate is less than 50 ° C./min, the degree of crystallinity increases and it is difficult to obtain a sheet suitable for stretching. As a cooling method, a method of directly contacting cold air, cooling water, or other cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used. The draft ratio ((rolling speed of the roll) / (flow rate of the resin flowing out from the die lip converted from the density)) is preferably 10 to 600 times, more preferably 20 from the viewpoint of air permeability and moldability. It is -500 times, More preferably, it is 30-400 times.

In this case, when the hole forming agent (d1) is used, it is preferably cooled to 25 ° C. or lower. On the other hand, when the β crystal nucleating agent (d2) is used, the β crystal ratio of the polyolefin (b) is adjusted to a range of 20 to 100%, preferably 50 to 100%. It is preferable to cool, and it is further preferable to cool to the range of 90-140 degreeC.
Step (4) and other processing steps thereafter can be performed in the same manner as in production method 1.

<Microporous membrane>
The microporous membrane of the present invention is obtained by melt-kneading the thermoplastic resin (a) and the polyolefin at a temperature higher by 10 ° C. or more than the melting point of the thermoplastic resin (a) in both of the above production methods 1 and 2. By applying stress to the polyolefin and the thermoplastic resin (a) in the molten state, the thermoplastic resin (a) can be formed into needles. The microporous membrane of the present invention is characterized in that the thermoplastic resin (a) having a needle-like structure is uniformly dispersed in a polyolefin as a matrix, and further, the thermoplastic resin (a) having a matrix and a needle-like structure is further provided. It is preferable to form a morphology in which the interfaces of the microporous membranes are in close contact with each other because the thermal shrinkage of the microporous membrane can be suppressed and the thermal shrinkage can be further improved.

The microporous membrane according to a preferred embodiment of the present invention has the following physical properties.
(1) The thickness of the microporous membrane obtained by the production method of the present invention is not particularly limited, and may be in the range of 5 to 200 μm as required for its use, but generally 5 to 50 μm. More preferably, it is 8-40 micrometers, More preferably, it is 10-30 micrometers.
(2) Gurley air permeability is in the range of 50 to 800 s / 100 ml.
(3) The shutdown temperature is in the range of 130 to 150 ° C.
In order to obtain such a microporous film, as a sheet material that is an intermediate material before forming micropores,
(4) The heat shrinkage rate at 200 ° C. is 30% or less before heat setting and 25% or less after heat setting.
(5) As the mechanical strength, for example, the tensile strength is 20 MPa or more.
(6) The film thickness unevenness of the sheet is small, and breakage during hot stretching can be prevented.

  Since the microporous membrane of the present invention has an excellent balance of compression resistance, heat resistance and permeability, it can be suitably used as a separator used in non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. It can be more suitably used as a single-layer separator for a nonaqueous electrolyte secondary battery.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
By the following method, a sheet was prepared with the composition excluding the pore-forming agent (d1), and the thermal shrinkage rate and mechanical strength were measured by the following methods. As a result, the resin does not depend on factors depending on the type and amount of the pore-forming agent (d1) not included in the microporous membrane, and on structural factors such as the shape and density of the microporous material formed by the pore-forming agent. The performance relating to the resin composition of the composition (α) itself was evaluated.

(Examples 1-8, Comparative Examples 1-3)
Polyphenylene sulfide resin, polyolefin resin-1 and thermoplastic elastomer shown in Tables 1 to 3 below were uniformly mixed with a tumbler to obtain a compounding material. Thereafter, the blended material is put into a twin-screw extruder with a vent (“TEX-30” manufactured by Nippon Steel Co., Ltd.) and melt kneaded (resin component discharge rate 20 kg / hr, screw rotation speed 350 rpm, resin component discharge rate) 0.057 (kg / hr / rpm) at a maximum torque of 60 (A), the set resin temperature is shown in Tables 1 to 3 “Step 1: Cylinder temperature”, and the die hole diameter is 3 mm. A strand is prepared while cutting so that the hole diameter (nozzle diameter) of the die and the diameter of the strand (that is, the strand diameter) are the same as those shown in Tables 1 to 3 "Die hole diameter / Strand diameter" Got. The strand diameter is a value obtained by measuring the diameter of the pellet after cutting using a caliper.

  Subsequently, the pellet of the resin composition obtained in the above step and the polyolefin resin-2 described in Tables 1 to 3 were combined with a vented twin screw extruder (“TEX-” manufactured by Nippon Steel Works, Ltd.). 30 ”), melt kneading (resin component discharge rate 15 kg / hr, screw rotation speed 200 rpm, resin component discharge rate 0.075 (kg / hr / rpm), maximum torque 60 (A), set resin temperature is Tables 1 to 3 below (see “Step 2: Cylinder temperature”) were prepared. Subsequently, T-die extrusion was performed to a film thickness of 0.1 mm, and with a cooling roll temperature-controlled at 80 ° C., the gap (lip width) of the lip portion of the T-die and the film thickness of the gel sheet were The gel-like sheet | seat was produced while cooling so that it might become Table 1-3 "lip width / sheet thickness". In addition, the thickness of the sheet | seat thru | or film | membrane was measured using the film thickness meter (The Digimatic indicator "ID-130M" by Mitutoyo Corporation).

  Subsequently, the obtained gel-like sheet was cut out to 60 mm × 60 mm, set in a biaxial stretching test apparatus, heated from room temperature to 120 ° C., and then perpendicular to the flow direction (MD) and MD when formed into a sheet. Simultaneously biaxial stretching was performed so that the stretching ratio in the direction (TD) was 3 times to obtain a stretched sheet. The obtained stretched sheet was heat-set at 125 ° C. for 10 minutes while being held by a tenter stretching machine to produce a sheet specimen having a thickness of 0.03 mm.

(Tensile strength)
The sheet specimens obtained in Examples 1 to 8 and Comparative Examples 1 to 3 are punched into a dumbbell shape of specimen type 5 in accordance with JIS-K7127 “Plastic—Testing Method for Tensile Properties”, and the tensile strength is set. It was measured. The results are shown in Tables 1-3.

(Heat shrinkage)
The sheet specimens obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were cut into 50 mm × 50 mm, and the heat shrinkage ratio was determined by a method in accordance with JIS-K7133 “Plastic-Film and Sheet—Heating Dimensional Change Measuring Method”. Was measured. The results are shown in Tables 1-3.

(Confirmation of PPS resin shape and calculation of aspect ratio)
The sheet test piece was cut with a cryomicrotome in the flow direction (MD) and the vertical direction (TD) when the sheet was made into a sheet, and this cut section was then scanned with a scanning electron microscope (SEM-EDS “JSM-” manufactured by JEOL Ltd.). 6360A "), arbitrary 10 points in the image were extracted, and the shape was observed. At that time, the longest part of the PPS resin particles was defined as the long side, the length in the direction perpendicular to the long side at a distance half the long side was defined as the short side, and the number average of the long side / short side was calculated as the aspect ratio.

※表中の各組成成分の配合割合に関する数値は質量部を表す。以下同じ。

* Numerical values related to the blending ratio of each composition component in the table represent parts by mass. same as below.

  Subsequently, a microporous film was prepared by the following method, and the film thickness, air permeability, and shutdown temperature were measured by the following method.

(Examples 9-16, Comparative Examples 4-6)
Polyphenylene sulfide resin, polyolefin resin-1 and thermoplastic elastomer shown in Tables 4 to 6 below were uniformly mixed with a tumbler to obtain a compounding material. Thereafter, the blended material is put into a twin-screw extruder with a vent (“TEX-30” manufactured by Nippon Steel Co., Ltd.) and melt kneaded (resin component discharge rate 20 kg / hr, screw rotation speed 350 rpm, resin component discharge rate) 0.057 (kg / hr / rpm) at a maximum torque of 60 (A), the set resin temperature is shown in Tables 4 to 6 “Step 1: Cylinder temperature”, and the die hole diameter is 3 mm). Strands were prepared while being pulled so as to obtain 4 to 6 “die hole diameter / strand diameter”, and cut to obtain pellets of the resin composition.

  Subsequently, pellets of the resin composition obtained in the above step, polyolefin resin-2 described in Tables 4 to 6 and pore forming agent (liquid paraffin and bis (2-ethylhexyl) phthalate blended in equal amounts) To a twin-screw extruder with a vent equipped with a T-die (“TEX-30” manufactured by Nippon Steel Works, Ltd.) and melt-kneaded (resin component discharge rate 15 kg / hr, screw rotation speed 200 rpm, resin component A melt-kneaded material was prepared with a discharge amount of 0.075 (kg / hr / rpm), a maximum torque of 60 (A), and a set resin temperature of the following Tables 4 to 6 “Step 2: Cylinder Temperature”. Subsequently, T-die extrusion molding was performed so that the film thickness was 0.1 mm, and cooling was performed while taking up the lip width / sheet thickness of Tables 4 to 6 with a cooling roll adjusted to 80 ° C. to form a gel. A sheet was produced.

  Subsequently, the obtained gel-like sheet was cut out to 60 mm × 60 mm, set in a biaxial stretching test apparatus, heated from room temperature to 120 ° C., and then perpendicular to the flow direction (MD) and MD when formed into a sheet. Simultaneously biaxial stretching was performed so that the stretching ratio in the direction (TD) was 3 times to obtain a stretched sheet. The obtained stretched sheet is fixed to a 20 cm × 20 cm aluminum frame, and then contains methylene chloride (surface tension 27.3 mN / m (25 ° C.), boiling point 40.0 ° C.) adjusted to 25 ° C. It is impregnated in a hole-forming agent removal bowl, and the hole-forming agent is removed while rocking at 100 rpm for 10 minutes. Further, after air-drying at room temperature, it is heat-fixed at 125 ° C. for 10 minutes while being held by a tenter stretching machine. As a result, a microporous film having a thickness of 0.03 mm was produced.

(Gurley air permeability)
The Gurley air permeability of the microporous film was measured according to JIS-P8117 “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method”. The results are shown in Tables 4-6.

(Shutdown temperature)
The microporous membrane was exposed to a hot air dryer set to a predetermined temperature for 1 minute, and the temperature at which the Gurley air permeability was 10,000 s / 100 ml or more was defined as the shutdown temperature. The results are shown in Tables 4-6.

※表中の各組成成分の配合割合に関する数値は質量部を表す。以下同じ。

* Numerical values related to the blending ratio of each composition component in the table represent parts by mass. same as below.

Each composition in Tables 1-6 is as follows.
PPS (a1) “MA-520” manufactured by DIC Corporation, linear type, V6 melt viscosity 150 [Pa · s]
PPS (a2) “MA-505” manufactured by DIC Corporation, linear type, V6 melt viscosity 45 [Pa · s]
Polyolefin (b1) “HI-ZEX 5305EP” manufactured by Prime Polymer Co., Ltd., MI = 0.8 (g / 10 min)
Polyolefin (b2) “HI-ZEX 3600F” manufactured by Prime Polymer Co., Ltd., MI = 1.0 (g / 10 min)
Compatibilizer (c1) “Bond First-E” manufactured by Sumitomo Chemical Co., Ltd. (thermoplastic elastomer made of ethylene / glycidyl methacrylate (88/12 mass%) copolymer)
Compatibilizer (c2) Copolymer obtained by grafting polystyrene at a mass ratio of 7: 3 to “Modiper A4100” (ethylene / glycidyl methacrylate (85/15 mass%) copolymer manufactured by NOF Corporation) Thermoplastic elastomer)
Polyolefin (e1) “HI-ZEX 5305EP” manufactured by Prime Polymer Co., Ltd., MI = 0.8 (g / 10 min)

1: PPS resin having a needle-like structure 1 ′: PPS resin having a spherical structure

Claims (21)

A microporous film comprising a thermoplastic resin having a melting point of 220 ° C. or higher, a polyolefin, and a compatibilizer, wherein the thermoplastic resin has a needle-like structure ,
A porous film , wherein the thermoplastic resin having a melting point of 220 ° C. or higher is a polyarylene sulfide resin, and the polyolefin is polyethylene .   The microporous membrane according to claim 1, wherein the thermoplastic resin has an aspect ratio in the range of 1.1 to 100.   The composition ratio of the thermoplastic resin and polyolefin is in the range of 1 to 73% by mass of the thermoplastic resin and 99 to 27% by mass of the polyolefin with respect to the total mass of the thermoplastic resin and polyolefin. The microporous membrane according to claim 1.   The composition ratio of the thermoplastic resin, the polyolefin, and the compatibilizer is such that the total mass of the thermoplastic resin and the polyolefin is 90 to 97% by mass with respect to the total mass of the thermoplastic resin, the polyolefin, and the compatibilizer, and The microporous membrane according to claim 1, wherein the compatibilizer is in the range of 10 to 3% by mass.   The microporous membrane according to claim 1, wherein the compatibilizing agent is a thermoplastic elastomer having a functional group having reactivity with the thermoplastic resin.   The separator for nonaqueous electrolyte secondary batteries which consists of a microporous film as described in any one of Claims 1-5.   The battery separator according to claim 6, wherein the battery separator is a single-layer separator for a nonaqueous electrolyte secondary battery. A thermoplastic resin (a) having a melting point of 220 ° C. or higher, a polyolefin (b), and a compatibilizer (c) are melt-kneaded at a temperature equal to or higher than the melting point of the thermoplastic resin (a) to obtain a resin composition (α ), The obtained resin composition (α) and the pore-forming agent (d1) or β-crystal nucleating agent (d2) at a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or more. A step (2) of obtaining a melt-kneaded product (β) by melt-kneading, forming a sheet of the melt-kneaded product (β) heated to a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher, and forming a needle-like structure A process for producing a microporous membrane comprising a step (3) of obtaining a sheet (γ) containing a thermoplastic resin (a) having a step (4) of making the obtained sheet (γ) porous ,
A method for producing a microporous membrane , wherein the thermoplastic resin having a melting point of 220 ° C. or higher is a polyarylene sulfide resin, and the polyolefin is polyethylene . Thermoplastic resin (a) having a melting point of 220 ° C. or higher, polyolefin (b), and compatibilizer (c), and a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher in an extruder having a die attached to the tip. After melt-kneading in (1), a strand is formed while taking up so that the die hole diameter / strand diameter is 1.1 or more, and then cut to obtain a resin composition (α) containing a thermoplastic resin (a) having an acicular structure (α) Step (1) for obtaining '), the obtained resin composition (α') and the pore-forming agent (d1) or β-crystal nucleating agent (d2) at a temperature equal to or higher than the melting point of the polyolefin (b) and Kneading at a temperature not higher than the melting point of the thermoplastic resin (a) to obtain a kneaded product (β ′) (2 ′), a temperature not lower than the melting point of the polyolefin (b) and the melting point of the thermoplastic resin (a) A kneaded product (β ') heated to the following temperature is made into a sheet and has a needle-like structure. A step (3 ′) for obtaining a sheet (γ) containing the thermoplastic resin (a) to be produced, and a step (4) for making the obtained sheet (γ) porous ,
A method for producing a microporous membrane , wherein the thermoplastic resin having a melting point of 220 ° C. or higher is a polyarylene sulfide resin, and the polyolefin is polyethylene .   In the step (1) or (1 ′), the charging ratio of the thermoplastic resin (a) and the polyolefin (b) is the total heat of the thermoplastic resin (a) and the polyolefin (b). The method for producing a microporous membrane according to claim 8 or 9, wherein the plastic resin (a) is in the range of 1 to 73 mass% and the polyolefin (b) is in the range of 99 to 27 mass%. In the step (2) or (2 ′),
The charging ratio of the resin composition (α) or the resin composition (α ′) to the hole forming agent (d1) is such that the resin composition (α) or the resin composition (α ′) and the hole forming agent ( The resin composition (α) or the resin composition (α ′) is in the range of 30 to 80% by mass and the pore-forming agent (d1) is 70 to 20% by mass with respect to the total mass with d1). Or
Or
The β crystal nucleating agent is in the range of 0.0001 to 10 parts by mass with respect to 100 parts by mass of the polyolefin (b) in the resin composition (α) or the resin composition (α ′).
The method for producing a microporous membrane according to claim 8 or 9.   In the step (2) or (2 ′), the resin composition (α) or the resin composition (α ′) and the pore-forming agent (d1) or the β crystal nucleating agent (d2) are further mixed with a polyolefin (e The method for producing a microporous membrane according to claim 8, wherein the mixture is melt kneaded.   In the step (2) or (2 ′), the thermoplastic resin (a) contained in the resin composition (α), the total mass (a + b + e) of the polyolefin (b) and the polyolefin (e), The polyolefin (e) is added so that the thermoplastic resin (a) is 1 to 73% by mass and the total amount (b + e) of the polyolefin (b) and the polyolefin (e) is in the range of 99 to 27% by mass. Item 10. The method for producing a microporous membrane according to Item 8 or 9. In the step (2), the obtained resin composition (α) and the pore-forming agent (d1) are melt-kneaded at a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher to obtain a melt-kneaded product ( The step of obtaining β), or the step (2 ′), the obtained resin composition (α ′) and the pore-forming agent (d1) at a temperature equal to or higher than the melting point of the polyolefin (b) and the thermoplasticity. Kneading at a temperature below the melting point of the resin (a) to obtain a kneaded product (β ′), and
The step (4) is a step (4a) of removing the hole forming agent (d1) after stretching the sheet (γ), and a step of stretching after removing the hole forming agent (d1) from the sheet (γ). The method for producing a microporous membrane according to claim 8 or 9, wherein the step (4c) is a step (4c) in which the pore-forming agent (d1) is removed and further stretched after the sheet (γ) is stretched.   In the step (1) or (1 ′), the thermoplastic resin (a) and the polyolefin with respect to the total mass (a + b + c) of the thermoplastic resin (a), the polyolefin (b) and the compatibilizer (c). The method for producing a microporous membrane according to claim 8 or 9, wherein the total mass (a + b) of (b) is in the range of 90 to 97 mass% and the compatibilizer (c) is in the range of 10 to 3 mass%. .   The method for producing a microporous membrane according to claim 8 or 9, wherein the compatibilizing agent is a thermoplastic elastomer (c1) having a functional group having reactivity with the thermoplastic resin (a).   In the step (1) or (1 ′), in addition to the thermoplastic resin (a) and the polyolefin (b), an antioxidant is further added in an amount of 0.01 to 5 masses per 100 mass parts of the polyolefin (b). The method for producing a microporous membrane according to claim 8 or 9, wherein the mixture is melt-kneaded in the range of parts.   The method for producing a microporous membrane according to any one of claims 8 to 17, wherein the microporous membrane is a separator for a nonaqueous electrolyte secondary battery.   The method for producing a microporous membrane according to claim 18, wherein the separator for a nonaqueous electrolyte secondary battery is a single layer separator for a nonaqueous electrolyte secondary battery. Thermoplastic resin (a) having a melting point of 220 ° C. or higher, polyolefin (b), and compatibilizer (c), and a temperature of the melting point of the thermoplastic resin (a) + 10 ° C. or higher in an extruder having a die attached to the tip. A resin composition (α ′) for a non-aqueous electrolyte secondary battery separator obtained by melt-kneading, forming a strand while taking up the die hole diameter / strand diameter to be 1.1 or more, and then cutting. The composition ratio of the thermoplastic resin (a) to the polyolefin (b) is such that the thermoplastic resin (a) is 1 to 1 with respect to the total mass (a + b) of the thermoplastic resin (a) and the polyolefin (b). In the range of 73% by mass and the polyolefin (b) in the range of 99-27% by mass,
The composition ratio of the thermoplastic resin (a), the polyolefin (b) and the compatibilizer (c) is the total mass (a + b + c) of the thermoplastic resin (a), the polyolefin (b) and the compatibilizer (c). ), The total mass (a + b) of the thermoplastic resin (a) and the polyolefin (b) is in the range of 90 to 97% by mass, and the compatibilizer (c) is in the range of 10 to 3% by mass. Yes,
Furthermore, the thermoplastic resin (a) has a needle-like structure ,
A resin composition for a separator for a non-aqueous electrolyte secondary battery , wherein the thermoplastic resin having a melting point of 220 ° C. or higher is a polyarylene sulfide resin, and the polyolefin is polyethylene .   The resin composition for a battery separator according to claim 20, wherein the separator for a non-aqueous electrolyte secondary battery is a single-layer separator for a non-aqueous electrolyte secondary battery.

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